The present invention relates to a method and apparatus of controlling an air conditioner, and more particularly relates to a method and apparatus of controlling the temperature of the indoor heat exchanger and/or the discharge temperature of the compressor of an air conditioner.
Generally, the air conditioner has a capacity of controlling the temperature of indoor heat exchanger and the discharge temperature of the compressor to or below predetermined values. FIGS. 9 and 10 illustrate typical examples of controlling compressors according to conventional methods. In these methods, the output frequency of the inverter is controlled according to detected temperature of discharge gas (hereinafter referred to as discharge temperature Td) of the compressor and detected temperature of the indoor heat exchanger (hereinafter referred as indoor heat exchanger temperature Tc) so that these temperatures are maintained at or below preset values. In FIGS. 9 and 10, the broken lines indicate actual variations of temperature whereas the solid line mean temperature variations per unit time.
In FIG. 9, when it is detected that the discharge temperature Td exceeds the set temperature T1 (time t1), the output frequency of the inverter is continuously decreased, so that the discharge temperature Td is dropped so as to be maintained within a safe range of a set temperature width .alpha. below the set temperature T1. When the discharge temperature Td drops below the safe range (time t3), the output frequency of the inverter is increased. After the output frequency turns to decrease, in this method of control the output frequency varies at a constant gradient even if the discharge temperature Td exceeds the set temperature T1 by a variation thereof (time t2).
The control method of FIG. 10 is the same as the control of FIG. 9 in that the output frequency of the inverter is decreased when the indoor heat exchanger temperature Tc exceeds the set temperature T1 in a heating operation, but in the method of FIG. 10, the output frequency of the inverter is dropped stepwisely for a predetermined time, 5 Hz for 20 seconds, for example. On the contrary, when the indoor heat exchanger temperature Tc drops below the set temperature T1, in this method the output frequency is continuously raised.
The control method of FIG. 9 is disadvantageous in that the frequency rather largely varies, and that hunting thereof frequently occurs. In hunting, the frequency becomes unstable. To draw the capacity of the air conditioner to the maximum it is preferable to maintain the discharge temperature Td and the indoor heat exchanger
temperature Tc closely to respective set temperatures but in practice there is a tendency such that the discharge temperature Td and the indoor heat exchanger temperature Tc are controlled below set temperatures. The control of FIG. 10 is superior to that of FIG. 9 in that the variation of the output frequency of the inverter is fairly small but there still remains a disadvantage in that any hunting of the frequency and a tendency of controlling the discharge temperature Td and the indoor heat exchanger temperature Tc below set temperatures are not improved.
This is because the controlled variables, the discharge temperature Td and the indoor heat exchanger temperature Tc each vary repeating fine hunting. More specifically, the discharge temperature Td and indoor heat exchanger temperature Tc actually finely vary about mean values as shown by broken lines in FIGS. 9 and 10 although they vary smoothly as indicated by solid lines when plotted as mean variations per unit time. The temperature sensor directly detects these fine variations, and the output frequency is varied according to detected variations. There is therefore a problem in that hunting of the frequency is not sufficiently prevented.